1. Field of the Invention
The invention relates to a method of producing a color-decorated injection molding.
2. Description of the Related Art
Injection molding technology is used for the large scale processing of thermoplastic molding compounds. Thermoplastics soften on heating and can be deformed in the plastic state. When a plunger injection molding machine is employed, the thermoplastic material is heated, preplastified by the plunger, and then pressed through channels or dies into a cooled mold. In the case of screw injection molding machines, the screw acts like a plunger and fills the mold so the material is plastified uniformly by the screw and a highly homogeneous temperature distribution is obtained.
An object of the invention is to provide a method by which color-decorated injection moldings having high physical and chemical quality and having good aesthetic effect can be produced. The colored decoration should, in particular, be of high strength and should give a high-grade visual impression.
European Patent Application No. EP 0 573 676 A1 describes the use of a support having a release characteristic for applying colored decoration to a substrate. In this prior art document, the colored decoration is first applied to a support having a release characteristic. A coating material is then applied over the colored decoration. The coating material is subsequently subjected to partial cross linking, and then, under pressure and/or elevated temperature, the partially cross linked coating material together with the colored decoration is transferred from the support to the substrate which is ultimately to be decorated. This transfer takes place in such a way that the coating material lies on the substrate under the colored decoration. Finally, further cross linking of the coating material takes place on the substrate.
U.S. patent application Ser. No. 08/946,802 filed Oct. 8, 1997 entitled xe2x80x9cMethod and Apparatus for Applying a Decoration to an Articlexe2x80x9d; U.S. Pat. No. 5,908,525 issued Jun. 1, 1999 and entitled xe2x80x9cMethod and Apparatus for Applying a Decoration to an Articlexe2x80x9d and U.S. Pat. No. 5,916,400 issued Jun. 29, 1999 and entitled xe2x80x9cMethod and Apparatus for Manipulating and Article for Applying a Decoration Thereonxe2x80x9d are hereby incorporated by reference.
The invention achieves the above-mentioned object by the following steps:
a) coating a plastics film with a colored decoration having dye molecules,
b) supporting the coated plastics film in an injection molding apparatus,
c) back spraying the plastics film with plastic in the injection molding apparatus, and
d) increasing the temperature to promote diffusion of dye molecules into the plastic.
The method of the subject invention can be used to produce large quantities of injection moldings in a cost effective operation to produce high quality parts. Examples of such moldings include, among others, automotive parts, housings for electronic appliances, sheets, and elements for the construction industry.
Particularly suitable materials for the plastics film upon which a colored decoration may be deposited are thermoplastics, especially polycarbonate and, polymethyl methacrylate (PMMA). It is also possible to use a plastics film made from polyolefins or copolymeric polyolefins and mixtures thereof. A preferred plastics film material is ethylene-styrene interpolymer, which is also identified by the name ESI and manufactured by the DOW Chemical Company. This film is a copolymeric polyolefin.
The thickness of the plastics film may be from 0.0002 to 0.002 inches (50 to 500 xcexcm).
To improve the quality of the colored decoration, the colored decoration may be transferred from a support onto the plastics film. The support has release characteristics which promote removal of the decoration from the support.
Supports having release characteristics are known and are illustrated in European Patent Application No. EP 0 573 676 A1. Particularly suitable sheetlike supports having release characteristics are certain papers or plastics films whose surface is designed or has been treated so that color layers or coating films applied under defined conditions can be transferred to an article or film by a kind of xe2x80x9cpeelingxe2x80x9d process which is similar to the process for peeling a decal. For the present invention, particularly suitable supports having such release characteristics are plastics films and especially polyester films. To promote peeling, the prior art has also disclosed appropriate release coats for a film having a release characteristic.
The diffusion of the dye molecules of the colored decoration takes place preferably at elevated temperatures from 356 to 572xc2x0 F. (180 to 300xc2x0 C.) and depends on the properties of the plastics used. This color diffusion takes place both into the plastics film and into the back sprayed plastic. The color diffusion generates a depth effect of the resulting colored decoration of the injection molding, since the dye molecules diffuse different distances in the plastic depending on their molecular weight. The result is an aesthetically appealing, high-quality decoration.
The increase in temperature can be carried out at least in part during the back spraying operation, or thereafter.
In a preferred embodiment a coating film is applied to the colored decoration after the colored decoration has been applied to the plastics film. The coating film is preferably also colored to provide a base color for the injection molded part. Within the injection molding apparatus, the coating film lies above the colored decoration. Below the colored decoration lies the plastics film such that the coating film directly faces the injection molding material. The coating film imparts a base color to the injection molding material. Superimposed on this base color is the colored decoration having dye molecules which diffuse a greater or lesser distance into the overlying plastics film.